1. Field of the Invention
The present invention relates to optical communication equipment.
2. Description of the Related Art
FIG. 1 shows a representative switch 100 of the prior art for routing data in a modem communication system. Switch 100 is a 3xc3x973 switch that can route data from any one of its three inputs to any one of its three outputs. Switch 100 comprises a 3xc3x973 arrayed waveguide grating (AWG) 104, three transmitter cards 106 coupled to input ports of AWG 104, and three receivers 130 coupled to output ports of AWG 104. Each transmitter card 106 is configured to receive a corresponding electrical stream of data, convert it into an optical signal, and send that optical signal to AWG 104. AWG 104 is a solid state device configured to redirect light entering any one of the input ports to a selected output port based on its wavelength. Each receiver 130 is configured to receive an optical signal from one of the output ports of AWG 104 and convert it back into a corresponding electrical data stream.
Each transmitter card 106 comprises a tunable laser 110 and a modulator 120. Laser 110 feeds an optical carrier signal into modulator 120. Modulator 120 modulates the carrier signal with data based on the corresponding electrical input data stream to produce an optical data-modulated output signal of the respective transmitter card 106. Each transmitter card 106 can be configured to send data to any chosen receiver 130 by setting the wavelength of laser 110 to the value for the corresponding output port of AWG 104. Depending on the implementation of AWG 104, lasers 110 corresponding to different input ports of AWG 104 may be tunable over different wavelength ranges.
The capacity of a switch, such as switch 100, defined as the number of ports multiplied by the throughput of each port is measured, e.g., in Gigabits per second (Gb/s). To meet the demands of ever-increasing data traffic in communication networks, switches of relatively large capacity are desirable. However, direct scaling of the switch architecture illustrated in FIG. 1 may not increase the switch capacity in proportion to the increasing switch size because the switch capacity is a convoluted function of many different parameters. For example, any one or a combination of the following may limit the capacity of switch 100: (i) the tuning range of lasers 110; (ii) the physical dimensions of the wafer on which AWG 104 is implemented and therefore the number of AWG channels; and/or (iii) the tolerable level of inter-channel crosstalk.
According to certain embodiments, the present invention provides a parallelized switch of increased capacity. The switch employs two or more parallel optical switch fabrics, e.g., arrayed waveguide gratings (AWG), combined with a set of transmitter cards. Each transmitter card has a tunable laser and two or more modulators, each configured to modulate a different copy of the output of the laser with a different set of data. Outputs of the modulators in each transmitter card are coupled to a set of corresponding input ports in the AWGs. A set of receiver cards, each receiver card having a number of receivers matching that of modulators in the transmitter cards, is coupled to output ports of the AWGs, such that each receiver card receives signals from a set of corresponding output ports in the AWGs. Each transmitter card can be configured to send data to any receiver card by setting the wavelength of its laser to the value corresponding to the set of output ports in the AWGs coupled to that receiver card. A parallelized switch of the present invention may be optimized based on a desired set of criteria, e.g., capacity, cost, and/or size.
According to one embodiment, the present invention is an apparatus, comprising: (A) J optical switch fabrics (OSF), each OSF having N input ports and N output ports and configured to route optical signals from the input ports to the output ports based on wavelength, where J and N are integers greater than one; (B) N transmitter cards, each transmitter card comprising a tunable laser and J modulators, each modulator configured to modulate a signal generated by said tunable laser with data, wherein the J modulators are coupled to J corresponding input ports of the J OSFs; and (C) N receiver cards, each receiver card comprising J receivers coupled to J corresponding output ports of the J OSFs, wherein the apparatus is configured to route data from any transmitter card to any receiver card.
According to another embodiment, the present invention is a method of transmitting data, comprising the steps of: (i) modulating an optical signal generated by a tunable laser with data using J modulators to produce J data-modulated optical signals, where J is an integer greater than one; and (ii) routing the J data-modulated optical signals using J optical switch fabrics (OSF), wherein: each OSF has N input ports and N output ports and is configured to route optical signals from the input ports to the output ports based on wavelength, where N is an integer greater than one; and the J modulators are coupled to J corresponding input ports of the J OSFs.